Surface treated steel sheet for battery containers, a battery container, and a battery produced thereof

ABSTRACT

A steel sheet for a battery container is covered with nickel-tin alloy layer on one side to be the inner side of the battery container which is formed by drawing the steel sheet. A battery using the steel sheet is manufactured by firstly filling positive electrode mix consisting of manganese oxide, graphite and potassium hydroxide and secondly filling negative electrode active material consisting of zinc and potassium hydroxide in the battery container.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a division of copending parent applicationSer. No. 08/633,715, filed Jun. 26, 1999, now U.S. Pat. No. 5,993,994which is a 371 of PCT/JP94/01656, filed Oct. 3, 1994.

FIELD OF THE INVENTION

The present invention relates to a surface treated steel sheet forbattery containers, a battery container and a battery using the batterycontainer. It especially relates to a surface treated steel sheet forbattery containers for an alkali manganese battery, a battery containerusing the surface treated steel sheet and a battery using the batterycontainer.

THE BACKGROUND ART

So far, the post-plating method wherein a drawn container produced fromcold rolled steel strip is plated in barrel plating or pre-platingmethod where a nickel plated steel strip is drawn into a batterycontainer have been employed for battery containers used for primarybatteries such as alkali manganese batteries, secondary batteries suchas nickel cadmium batteries, and a nickel-hydrogen battery that isexpected to be increasingly in demand as a new secondary battery, inwhich a strong basic solution is packed. The reasons why nickel platingis employed for battery containers such as those of alkali manganesebattery or nickel cadmium battery are as follows:

1) a strong basic solution of potassium hydroxide is used as anelectrolyte in these batteries, and nickel has excellent corrosionresistance to alkaline solutions.

2) nickel has stable contact resistance when a battery is connected toan external terminal.

3) spot welding is practiced when component parts are welded andassembled into batteries in the battery manufacturing process or whenbatteries are serially connected in order to increase voltage or whenthey are connected in parallel in order to allow large current flow, andnickel has also excellent weldability.

However, barrel plating causes unstable quality due to insufficientplating thickness and the difficulty of uniform deposition caused byinsufficient circulation of plating solution deep into the bottomportion of the battery container when the inside of a tall cylindricalbattery container is plated by barrel plating. On the other hand,although the above-mentioned problems are not caused in the pre-platingmethod, the battery container produced from a nickel-plated steel sheetthat is treated by thermal diffusion has improved corrosion resistancebecause the nickel plating layer is recrystallized and softened and thushas good extensibility, but it has poor adhesion to the positiveelectrode mix because the inner surface of the positive electrodecontainer (the battery container of the present invention) has smallcracks and a smooth surface after drawing.

Thereupon, battery performance has a close relationship to theproperties of the inner surface of the positive electrode container (thebattery container of the present invention) in alkali manganese battery(see FIG. 2). The better the adhesion of the positive electrode mix(composed of manganese dioxide as the positive electrode activematerial, graphite as the conducting material and potassium hydroxide asthe electrolyte) of the alkali manganese battery to the inner surface ofthe battery container, the better the battery performance. In the caseof alkali manganese battery, the positive electrode mix contacts withthe battery container and the battery container functions not only as acontainer but also as an electrical conductor that transmits electrons.Therefore, when the contact resistance between the positive electrodemix and the inner surface of the battery container is large, theinternal resistance of the battery is likewise large, and batteryperformance is deteriorated by the resultant drop of current orreduction of discharge duration. Therefore, it is preferable to reducethe contact resistance between the positive electrode mix and the innersurface of the battery container as little as possible in order toobtain a high performance battery.

Alkali manganese battery is superior to manganese battery inperformancing high load electrical discharge where there is anespecially large current flow, and the battery performance of the alkalimanganese battery can be improved by reducing internal resistance of thebattery. For the purpose of reducing the contact resistance between thepositive electrode mix and the battery container to enable a largecurrent flow, several methods such as roughening the inner surface ofthe battery container, providing grooves on the inner surface of thebattery container in the lengthwise direction, and coating a conductivematerial composed of graphite added by binder on the inner surface ofthe battery container etc., are proposed. (See Battery Handbook, page84, issued by MARUZEN in 1990)

Improvement in the contact between the positive electrode mix and thebattery container causes a reduction of internal resistance, andconsequently larger battery capacity can be obtained by reducing theamount of graphite in the positive electrode mix and increasing theamount of manganese dioxide as the positive electrode active material.Thus, battery performance depends considerably on the improvement of theinternal resistance and particularly, the contact between the batterycontainer and the positive electrode mix.

However, the use of a roughened punch in order to roughen the innersurface of the battery container causes the problem where the rougherthe punch, the lower the drawability, and the punch can not be roughenedbeyond a certain extent.

Also, the use of a steel substrate having larger crystal grains toroughen the inner surface of the battery container after drawing causesthe problem that the larger crystal grains result in a roughened surfaceat the positive electrode terminal and a deteriorated appearance for thebattery container product in the case of a pip type battery that isrecently dominant (the part of the positive electrode terminal of thebattery container is convexly shaped).

Further, although a conductive paint coating or conductive materialcoating on the inner surface of the battery container can reduceinternal resistance, it also causes disadvantages such as an increase inthe process of the battery manufacturing and an increase in productioncost.

Therefore, a battery material having a low cost of manufacture and lowinternal resistance is required for high performance alkali manganesebatteries.

INDICATION OF THE INVENTION

The surface treated steel sheet for a battery container of the presentinvention has one of the following structures:

1) nickel-tin alloy layer is formed as the uppermost layer on thesurface that is to become the inner surface of a battery container

2) nickel-tin alloy layer as the uppermost layer and nickel layer as thelower layer are formed on the surface that is to become the innersurface of a battery container

3) nickel-tin alloy layer as the uppermost layer, nickel layer as theintermediate layer and nickel-iron alloy layer as the lowermost layerare formed on the surface that is to become the inner surface of abattery container

4) nickel-tin alloy layer as the uppermost layer and nickel-iron alloylayer as the lower layer are formed on the surface that is to become theinner surface of a battery container

5) nickel-tin alloy layer as the uppermost layer, iron-nickel-tin alloylayer as the intermediate layer and nickel-iron alloy layer as thelowermost layer are formed on the surface that is to become the innersurface of a battery container

6) nickel-tin alloy layer as the uppermost layer, nickel layer as theintermediate layer and nickel-iron alloy layer as the lowermost layerare formed on the surface that is to become the outer surface of abattery container

7) nickel-tin alloy layer as the uppermost layer and nickel layer as thelower layer are formed on the surface that is to become the outersurface of a battery container

8) nickel layer is formed as the uppermost layer on the surface that isto become the outer surface of a battery container

The battery containers of the present invention are produced by drawingany surface treated steel sheet mentioned above in 1) to 8).

The batteries of the present invention are produced using theabove-mentioned battery containers, and the positive electrode mix(manganese dioxide+graphite as conductive material+potassium hydroxidesolution as electrolyte) is packed on the positive electrode side andthe negative electrode gel (granular zinc+potassium hydroxide solutionas electrolyte) is packed on the negative electrode side in the batterycontainer.

Batteries having the structures mentioned above can have excellentbattery performance such as a low internal resistance in the battery, alarge short-circuit current and long discharge duration.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a process flow diagram of a manufacturing process for asurface treated steel sheet of the present invention.

FIG. 2 shows a cross sectional view of a battery of the presentinvention.

FIGS. 3a and 3b are observation photographs taken of the inside ofbattery containers.

THE BEST CONDITION FOR PRACTICING THE INVENTION

The present invention is described below in detail.

First of all, the surface treated steel sheet of the present inventionis explained.

The surface treated layer of the steel sheet of the present inventionhas a different structure of surface the treated layer on either sidethat is to become the inner surface of the battery container or the sidethat is to become the outer surface of a battery container as mentionedpreviously.

At first, the structure of the surface treated layer on the side that isto become the inner surface of a battery container. On the side that isto become the inner surface, nickel-tin alloy layer or iron-nickel-tinalloy layer is formed. The reason why these alloy layers are formed onthe inner surface of a battery container is to cause numerous microcracks in these layers when the surface treated steel sheet is drawninto a battery container. And another reason why these alloy layers areformed on the inner surface of a battery container is because when thesteel substrate comprising a battery container is exposed on the surfaceof the battery container, the positive electrode mix will react with theiron present and form iron oxide, which serves to increase the internalresistance of the battery and cause a deterioration of the batteryperformance in the case of alkali manganese batteries.

The thickness of the above-mentioned nickel-tin alloy layer oriron-nickel-tin layer is preferably in the range of 0.15 to 3.0 μm, morepreferably 0.2 to 2.0 μm. When the thickness of the alloy layer is lessthan 0.15 μm, smaller cracks are formed in the alloy layer in thedrawing process, and the adhesion of the surface treated layer to thepositive electrode mix is not improving, and consequently the internalresistance of the battery is not reduced. On the other hand, when thethickness of the alloy layer is more than 3.0 μm, the effect of theimproving adhesion of the surface treated layer to the positiveelectrode mix becomes saturated and cost effectiveness is lost.

The nickel-tin alloy layer can be formed either by nickel-tin alloyplating or by a process comprising a prior nickel plating and prior tinplating followed by heat treatment, which causes diffusion of tin intonickel, and the resulting formation of nickel-tin alloy layer.

In addition, it is preferable that the nickel layer and/or iron-nickelalloy layer is formed under the nickel-tin alloy layer for the purposeof improving the adhesion of the nickel-tin alloy layer to the steelsubstrate as well as improving the corrosion resistance of the entiresurface treated steel sheet. Although the thickness of these layers arenot particularly defined, a thickness less than 3 μm is preferable basedon economic considerations.

Secondly, the structure of the surface treated layer on the side that isto become the outer surface of a battery container is explained. Thereason why nickel layer is formed on the outer surface of a batterycontainer is as follows:

As the outer surface of a battery container is to be junction which isconnected with an external terminal, a small and stable contactresistance and excellent corrosion resistance are required for essentialperformance of the outer surface of the battery container.

Next, the manufacturing process for the surface treated steel sheet isdescribed based on FIG. 1.

[Steel Sheet]

Aluminum killed steel is generally preferred as the substrate forplating. Non-aging hyper low carbon steel with added niobium, boron ortitanium can be available. Usually, a steel strip that iselectrolytically cleaned, annealed and skin-passed after being coldrolled is used as the substrate for plating.

[Nickel Plating]

After pre-treatment consisting of electrolytic cleaning in alkalisolution, rinsing in water, pickling in sulfuric acid or hydrochloricacid (electrolytic or dipping) and rinsing in water, the above-mentionedsteel substrate for plating is plated with nickel. Any known nickelplating bath such as Watt bath, sulfamic acid bath or chloride bath canbe used. Also, any type of nickel plating such as mat plating,semi-gloss plating or gloss plating can be formed. Improvement inbattery performance can be particularly expected using the gloss platingof these platings. The gloss plating process uses the plating bathcomprising a nickel plating solution with an added organic compoundcontaining sulfur (benzene-sulfonic acid derivatives such as sodiumbenzene-sulfonate or paratoluonesulfonamide, or saccharin), which givesluster to the plating by depositing finely plated crystals and byleveling the plating layer. And the gloss plating also causes anextremely hard plating layer.

The gloss plating process mentioned hereupon can be any one of thefollowing processes:

1) the one wherein a glossy nickel plating layer is directly formed onthe steel substrate by gloss plating;

2) the one wherein a mat finished nickel plating layer is formed on thesteel substrate by mat plating followed by plating a glossy nickelplating layer on top;

3) the one wherein a semi-glossy finished nickel plating layer is formedon the steel substrate by semi-gloss plating followed by plating aglossy nickel plating layer on top.

Tin plating on the glossy nickel plating layer plated on the steelsubstrate followed by heat treatment is preferable because scaly cracksare also formed in the glossy nickel plating layer when the plated steelsubstrate is drawn, and then numerous cracks are formed in the entireplating layer accompanied by micro cracks formed in the tin nickelplating layer, namely, the crack density increases.

In the present invention, a steel sheet is plated with nickel either onboth sides or only one side by a nickel plating selected from methods 1)to 3) mentioned above.

The thickness of the nickel plating layer plated on a surface that is tobecome the outer side of the battery container is in the range of 0.5 to5 μm, preferably 1 to 4 μm. In the case where nickel is plated on onlyone side of a steel sheet, it is plated on the surface that is to becomethe outer side of the battery container.

The thickness of the nickel plating layer plated on a surface that is tobecome the inner side of the battery container is preferably in therange of 0.5 to 4 μm, more preferably 1 to 3 μm from the view point ofharmony between battery performance and cost efficiency. When theabove-mentioned thickness of the nickel plating is less than 0.5 μm onthe inner surface of the battery container, numerous pinholes are formedin the nickel plating layer, which undesirably cause the increaseddissolution of iron (steel sheet) into the alkali solution, that is theelectrolyte solution within the battery, and the increased formation ofiron oxide.

The thickness of nickel plating less than 0.5 μm on the outer surface ofthe battery container is also undesirable because corrosion resistanceis apt to be deteriorated.

[Tin Plating]

The above-mentioned nickel plated steel sheet is followed by in platingthat is formed on both sides or the one side that is to become the innerside of the battery container.

While either of the usual acid bath or the usual alkaline bathavailable, stannous sulfate bath or phenolsulfonic acid bath ispreferably used in the present invention. When the tin plating layer isto be formed, the amount of tin plating is defined from the followingview point. In the present invention, the entire tin plating layershould be converted into a nickel-tin alloy layer by a heat treatmentwhich is used to form the nickel-tin alloy layer, for the reason thatwhen the tin plating layer remains in the nickel-tin alloy layer afterheat treatment, tin dissolves into the potassium hydroxide solution thatis the electrolyte of the alkali battery and hydrogen is generated,which deteriorates battery performance. Therefore, it is essential thatthe entire tin plating layer is converted into nickel-tin alloy by heattreatment. When the plated steel sheet is heated below 700° C. in theheat treatment process, the resultant nickel-tin alloy is mainlycomposed of Ni₃ Sn, Ni₃ Sn₂ and Ni₃ Sn₄. As Ni₃ Sn has the least amountof tin relative to nickel among these alloy composition, tin iscompletely alloyed with nickel by heat treatment when tin, which ispresent in an amount less than that found in Ni₃ Sn (atomic weight ratioof Ni:Sn is 3:1), is plated on a nickel plating, which the amount of Nipresent in an amount is more than that found in the Ni₃ Sn layer.Accordingly, the amount of tin should be less than 3 times the amount ofnickel by the atomic weight ratio of tin to nickel.

As the atomic weight of tin is 118.6 and that of nickel is 58.7, theatomic weight ratio of Ni:Sn is 3:1, so the ratio of amount oftin/amount or nickel is about 0.67 as shown in the following equation.

    The ratio of amount of tin/amount of nickel=118.6 (58.7×3)=0.67

When tin plating layer is formed at a larger ratio than thatmentioned-above (about 0.67), the nickel required for the formation ofthe nickel-tin alloy layer is insufficient at the time of alloyingtreatment (heat treatment), and the tin plating layer remains asmetallic tin as plated, which is not preferable for the presentinvention.

In other words, when nickel is present in an amount that is about 1.48(=1/0.67; inverse of above-mentioned value 0.67) times the amount of tinthat is plated, tin is totally alloyed into nickel-tin alloy during theheat treatment process, and tin does not remain as metallic tin, whichis preferable for battery performance.

[Nickel-Tin Alloy Plating Another Method by which A Nickel-Tin AlloyLayer is formed]

The above-mentioned method is one of the methods by which a nickel-tinalloy layer is formed, wherein after a tin plating layer is formed on anickel-plated steel sheet, the plated steel sheet is heat treated toform a nickel-tin alloy layer. In the present invention, another method,wherein a nickel-tin alloy layer is directly formed on a steel sheet, isproposed. The use of this method followed by heat treatment improvesshort circuit current in battery performance.

The steel sheet used as the substrate for the above-mentioned nickel-tinplating can suitably be selected from the following two kinds of steelsheets.

1) cold rolled steel sheet

2) steel sheet previously plated with nickel

As mentioned above, two types of method for forming a nickel-tin alloylayer are proposed, and heat treatment is used after plating by eitherthe first method or the second one because a nickel plating layer formedon the surface that is to become the outer side of the battery containercan be recrystallized and softened by heat treatment (which is helpfulfor improving corrosion resistance of the battery container).

The second mentioned method of nickel-tin alloy plating (another methodfor the forming nickel-tin alloy layer) is described below in detail.

Chloride-fluoride bath or pyrophosphoric acid bath is employed as a bathfor nickel-tin alloy plating. The nickel-tin alloy layer can be formedon one side of a cold rolled steel sheet as well as on both sides of it.The thickness of the nickel-tin alloy plating layer formed on one sideof the steel sheet is different from that formed on the other side ofthe steel sheet.

While a thickness range of 0.15 to 3.0 μm is preferable on the surfacethat is to become the inner side of the battery container, a thicknessin the range of 0.15 to 1.5 μm is preferable on the surface that is tobecome the outer side of the battery container from the view point ofcorrosion resistance and contact electrical resistance.

[Heat Treatment]

In the first mentioned method for forming a nickel-tin alloy layer,nickel is plated on both sides of a steel sheet followed by plating withtin on at least one side of the nickel plated steel sheet and then heattreating to form nickel-tin alloy. Alternatively, nickel is plated onboth sides of a steel sheet followed by heat treatment and then tinplating on at least one side of the nickel plated steel sheet followedby heat treatment to form a nickel-tin alloy. Furthermore, nickel can beplated on a steel sheet or on a nickel plated steel sheet followed byplating with nickel-tin alloy (the second method) and then heattreatment.

The heat treatment is preferably carried out under a non-oxidizing orreducing gas atmosphere in order to prevent the formation of an oxidefilm on the plated steel sheet. Heat treatment at about 200° C. producesa nickel-tin alloy layer. When attempting to improve the corrosionresistance of the plating layer, particularly on the outer side of thebattery container, by forming a nickel-iron diffusion layer between thenickel plating layer and the iron substrate (steel plate) accompanyingthe alloying treatment of nickel-tin alloy, heating at 450° C. or moreis required for the formation of a diffusion layer. More specifically,heat treatment is practiced in the temperature range of 450 to 850° C.for a period ranging between 30 seconds to 15 hours.

Either the box annealing process or the continuous annealing process canbe used as the heat treatment process, and the preferred conditions forheat treatment is at a temperature between 600 to 350° C. for 30 secondsto 5 minutes in the continuous annealing, and at a temperature between450 to 650° C. for 5 to 15 hours in the box annealing. In addition, aniron-nickel-tin alloy layer (3 component elements) can be formed betweenthe steel substrate and the plating layers of nickel and tin in thepresent invention. For this case, after plating nickel on the steelsubstrate followed by tin plating on the nickel plated steel substrate,heat treatment at rather high temperature for a longer period of timecauses the mutual diffusion of the 3 component elements.

[Skin Pass]

Skin pass is carried out for the purpose of preventing origination ofstretcher strains caused by heat treatment after nickel plating. Skinpass is carried out for the other purpose of obtaining a steel sheethaving a desired surface roughness or appearance such as bright finishor dull finish by using working rollers having different surfaceroughness in the skin pass process.

The present invention is described in more detail in the followingexamples.

MANUFACTURING OF SURFACE TREATED STEEL SHEET Example 1

A cold rolled and annealed aluminum killed low carbon steel sheet havinga thickness of 0.25 mm was used as a substrate for plating.

The chemical composition of the presented steel sheet is as weight % asfollows:

C:0.04%, Mn:0.19%. Si:0.01%, P:0.012%, S:0.009%, Al:0.064%, N:0.0028%

The steel sheet mentioned above was electrolytically degreased under theconditions described below.

(Electrolytical decreasing in alkali solution)

Electrolysis Conditions;

Bath composition: Sodium hydroxide 30 g/l

Current density and treatment time :

5 A/dm² (anodic treatment)×10 seconds and

5 A/dm² (cathodic treatment)×10 seconds

Bath temperature: 70° C.

After this treatment, the steel sheet was pickled in sulfuric acid(dipping in 50 g/l of sulfuric acid at 30° C. for 20 seconds), and thenplated with nickel under the conditions described below.

Bath composition Nickel sulfate 320 g/l

Boric acid 30 g/l

Sodium lauryl sulfate 0.5 g/l

Bath temperature: 55±2° C.

pH: 4.1˜4.6

Stirring: Air bubbling

Current density: 10 A/dm²

Anode: nickel pellet (nickel pellets were packed in a titanium basketand the basket was covered with a polypropylene bag.)

The steel sheet was mat nickel plated on one side or both sides, and thethickness of the plating layer was controlled by varying the duration ofelectrolysis under the above-mentioned conditions.

After nickel plating, the plated steel sheet was tin plated on one sideor both sides of the plated steel sheet in a stannous sulfate bath underthe conditions described below.

(Tin plating)

Bath composition Stannous sulfate 30 g/l

Phenolsulfonic acid 60 g/l

Ethoxylated α-naphthol 5 g/l

Bath temperature: 55±2° C.

Current density: 10 A/dm²

Anode: Plate of tin

Several types of samples having various plating thickness weremanufactured by varying the duration of electrolysis under theabove-mentioned conditions.

Next, after nickel and tin plating, the plated steel sheet was heattreated to form a nickel-tin alloy layer under the conditions describedbelow. The atmosphere for heat treatment was as follows

Protective gas composed of 6.5% hydrogen and residual nitrogen andhaving a dew point of -55° C. was used.

Several types of surface treated steel sheets were manufactured byvarying the soaking temperature and the soaking period. Thosemanufactured samples are shown as Sample 1 to 10 in Table 1. Thethickness of the nickel plating layer, the nickel-iron alloy layer andthe nickel-tin alloy layer shown in Table 1 were measured by GDS (Glowdischarge emission spectral analysis).

The surface analysis by x-ray diffraction analysis and GDS (Glowdischarge emission spectral analysis) of sample in which a nickelplating layer was covered with tin and then heat treated showed theformation of nickel-tin alloy. The sample was manufactured as follows: asteel sheet was plated with nickel to a thickness of 2 μm, and thenplated with tin to a thickness of 0.75 μm, and afterwards the platedsteel sheet was heat treated at 500° C. for 6 hours.

It was found by X-ray diffraction analysis that the nickel-tin alloylayer produced from a two layered plating comprising nickel layer andtin layer and was mainly composed of Ni₃ Sn. The hardening of theplating surface is supposed to be dependent on the precipitation ofthese inter metallic compounds. It was found that heat treatment at 300°C. for 6 hours mainly produced Ni₃ Sn₂ and that while heat treatment athigher temperatures produced an alloy layer richer in nickel content,heat treatment at lower temperatures produced an alloy layer richer intin content. Furthermore, it was confirmed by GDS (Glow dischargeemission spectral analysis) that heat treatment at 200° C. for 1 houralso produced a nickel-tin alloy layer.

Example 2

A surface treated steel sheet was manufactured using the same steelsubstrate as in Example 1 by the following manufacturing process whereinthe steel sheet was plated with semi-glossy nickel, then plated withglossy nickel and finally plated with tin under the same tin platingconditions as in Example 1 followed by heat treatment and skin pass.

The surface treated steel sheet was manufactured by a series ofprocesses consisting of semi-glossy nickel plating on both sides of thesteel sheet and subsequent glossy nickel plating on both sides of thesteel sheet under the following conditions after electrolyticaldegreasing in alkali solution and pickling in sulfuric acid under thesame conditions as described in Example 1.

1) Semi-glossy nickel plating

Bath composition : Nickel sulfate 300 g/l

Boric acid 30 g/l

Nickel chloride 45 g/l

Sodium lauryl sulfate 0.5 g/l

Brightener on the market 1.5 ml/l

(unsaturated alcohol and unsaturated carboxlic acid based)

Bath temperature: 55±2° C.

pH: 4.0 to 4.5

Stirring: Air bubbling

Current density: 15 A/dm²

2) Glossy nickel plating

Glossy nickel plating was practiced under the following conditions aftersemi-glossy nickel plating shown in 1).

Bath composition: Nickel sulfate 300 g/l

Boric acid 30 g/l

Nickel chloride 45 g/l

Sodium lauryl sulfate 0.5 g/l

Brightener on the market 1.0 ml/l

(Benzene sulfonic acid derivative)

Bath temperature: 60±2° C.

pH: 4.3 to 4.6

Stirring: Air bubbling

Current density: 10 A/dm²

Under the above-mentioned conditions, one side of the steel sheet wasonly plated with semi-glossy nickel and the other side of the steelsheet was plated with semi-glossy nickel and further plated with glossynickel on top.

Several types of samples having various nickel a plating thicknesses byvarying the electrolysis treatment time. The thus manufactured samplesare shown as samples 11 to 14 in Table 2.

Example 3

The steel substrate of Example 1 was mat nickel plated under the sameconditions as Example 1 and subsequently plated with nickel-tin alloyusing a chloride- fluoride bath. The conditions for nickel-tin alloyplating are as follows:

Bath composition: Stannous chloride 50 g/l

Nickel chloride 300 g/l

Sodium fluoride 30 g/l

Acid ammonium fluoride 35 g/l

Bath temperature: 65° C.

pH: 4.5

Current density: 4 A/dm²

Anode composed of nickel-tin alloy containing 28% tin was used. Severaltypes of samples having various thicknesses of nickel-tin alloy platingwas obtained by varying the electrolysis treatment time. The thusmanufactured samples are shown as samples 15 to 18 in Table 3.

(Explanation of the battery container)

Next, a method of manufacturing a battery container using theabove-mentioned surface treated steel sheets is described below.

The battery container of the present invention is produced from thesurface treated steel sheets manufactured as mentioned above by deepdrawing. The inventors of the present invention found that theapplication of the above-mentioned surface treated steel sheets as abattery container of alkali dry battery resulted in superior batteryperformance compared to using conventional battery containers.

(Inner surface structure of the battery container)

The internal resistance of an alkali manganese battery depends on thecontacting state of graphite as the conductive material in a positiveelectrode mix with the inner surface of the battery container. Namely,it is believed that the formation of uneven micro cracks on the innersurface the battery container provides a wider area for contacting ofthe positive electrode mix with the inner surface of the batterycontainer, which results in lower contact resistance and strongeradhesion, and consequently reduced internal resistance of the battery.

Hereupon, it is believed that the internal resistance is reduced by theremarkable improvement of adhesion of the positive electrode mix to theinner surface of the battery container as the result of the formation ofthe cracks caused by drawing the surface treated steel sheet having anextremely hard nickel-tin alloy layer. In order to confirm thishypothesis, the inner surfaces of the conventional battery container andthat of the present invention were observed under a microscope. Theresults are shown in FIGS. 3a and 3b. FIG. 3a shows the inner surface ofa conventional battery container produced by drawing a conventionalnickel plated steel sheet, in which unevenness is observed only in thelongitudinal direction of the container. FIG. 3b shows the inner surfaceof a battery container of the present invention which is produced bydrawing the surface treated steel sheet obtained by successively plating2 μm of nickel and 0.4 μm of tin on a cold rolled steel sheet, and thenforming a nickel-tin alloy layer by heat treatment of the plated steelsheet at 500° C. for 6 hours, in which numerous micro cracks havingdiameters of several μm are observed in the longitudinal direction ofthe container and in the circumferential direction as well. It isbelieved that the internal resistance of the battery is reduced by thepenetration of the positive electrode mix containing graphite powderinto the micro cracks formed on the inner surface of the container inthe longitudinal and circumferential directions. It is supposed that thereason why numerous micro cracks are formed on the inner surface of thedrawn container is because the nickel-tin alloy layer is hard andbrittle. This feature of hardness and brittleness was confirmed by thefollowing experiment.

A cold rolled steel sheet was successively plated with 2 μm of nickeland 1.6 μm of tin, and then heat treated at 500° C. for 6 hours. Thehardness of the surface layer was measured to have a value of 860 with amicro Vickers hardness tester (load: 10 g). On the other hand, thesurface hardness of a semi-glossy nickel layer having a thickness of 2μm was measured to have a value of 355 and that of a nickel layer havinga thickness of 2 μm followed by the same subsequent heat treatment at500° C. for 6 hours as described above was measured to have a value of195.

The results showed that the surface layer consisting of tin layer platedon nickel plating layer followed by heat treatment was remarkably harderthan those of 2 former surface layers (the one consisting of semi-glossynickel plating alone and the one consisting of semi-glossy nickelplating followed by heat treatment).

(Outer surface structure of the battery container)

Although the type of surface treatment layer formed on the outer surfaceof the battery container is not particularly defined in the presentinvention, it is preferable to form a nickel plating layer since a smallcontact resistance, which is invariable over time, is required on theouter surface of the battery container. Furthermore, it is alsopreferable to form a nickel-tin alloy layer on a nickel plating layer inthe present invention. As this alloy layer is extremely hard asmentioned above, scratch resistance is improved, and this can cover up afault that the nickel plating layer is apt to be scratched by thedrawing process or the battery manufacturing process as a result ofsoftening of the nickel plating layer especially when it is heat treatedto improve corrosion resistance after plating. A lower contactresistance is required on the outer surface of the battery container,and it can be attained by plating nickel-tin alloy on the surface thatis to become the outer surface of the battery container. In the casewhere a steel sheet is plated with 2 μm of nickel followed by platingwith 0.75 μm of tin on top and then heat treatment at 500° C. for 6hours, the contact resistance measured 1.8 m Ω by 4 probe method. On theother hand, the contact resistance of the steel sheet plated with 2 μmof nickel alone measured 3.5 m Ω. Therefore, it can be seen that anickel-tin layer is the surface treated layer having a lower contactresistance.

The preferable thickness of the nickel plating layer formed on the outersurface of the battery container is in the range of 0.5 to 5 μm, morepreferably in the range of 1 to 4 μm. It is preferable that this nickelplating layer is converted into a diffused nickel-tin alloy layer byheat treatment in order to improve corrosion resistance. when thenickel-tin alloy layer is formed on the inner surface of the batterycontainer, the thickness of this alloy layer is preferably in the rangeof 0.15 to 3 μm, more preferably in the range of 0.2 to 2 μm.Furthermore, when the nickel-tin alloy layer is formed on the outersurface of the battery container, the thickness of this alloy layer ispreferably in the range of 0.15 to 1.5 μm.

(Explanation of manufacturing of the battery container)

Battery containers for Tan-3 type (JIS LR-6) alkali manganese batterywere manufactured from the above-mentioned surface treated steel sheetby drawing.

At first, a circular blank was punched out from the above-mentionedsurface treated steel sheet, and then it was drawn. After that the upperopen edge portion of the battery container was trimmed off, and acylindrical container having 49.3 mm in longitudinal length and 13.8 mmin outer diameter was manufactured under an 8 stage drawing process.

(Battery manufacturing)

After manufacturing a battery container in the above-mentioned manner, aTan-3 type (JIS LR-6) alkali manganese battery was manufactured asfollows:

At first, manganese dioxide and graphite were gathered together at aweight ratio of 10:1, then they were added with potassium hydroxide (8mole) and all of them were mixed, and then the positive electrode mixwas prepared. Afterwards the positive electrode mix was pressed in ametal mold, then shaped in the positive electrode mix pellet having adoughnut shape and the prescribed dimensions, and then the thus producedpellets were compressively inserted into the battery container.Subsequently, the prescribed portion below the open edge of the batterycontainer was necked-in processed in order to install a negativeelectrode plate made by spotwelding some negative electrode collectingrods into the battery container. Afterwards, a separator produced from anon-woven fabric made of VINYLON was inserted into the battery containeralong the inner circumference of the inserted pellets that had beencompressively attached to the inner surface of the battery container,and then negative electrode gel composed of granular zinc and potassiumhydroxide saturated with zinc oxide was inserted into the batterycontainer. Finally, after the negative electrode plate installed with agasket made of insulating material was inserted into the batterycontainer, it was seamed with the battery container by caulking, tocomplete an alkali manganese battery.

In the case where graphite was coated on the inner surface of thebattery container, 80 parts by weight of graphite and 20 parts by weightof thermosetting epoxy resin were first dispersed in methyl ethylketone,then spray coated onto the inner surface of the battery containerfollowed by drying at 150° C. for 15 minutes.

The battery performance of a Tan-3 type alkali manganese batterymanufactured in the above-mentioned manner was measured after being keptat room temperature for 24 hours. Furthermore, in order to monitor anychange in the course of time, the battery performance was also measuredafter the battery was stored for a month (30 days) in athermo-hygrostatic room having a temperature of 60° C. and a humidity of90%. The battery performance was evaluated by measuring twocharacteristics of which one was the internal resistance (m Ω) by thealternating current impedance method (Frequency 1 kHz) and another wasthe short-circuit current (A) in which 1 m Ω was charged. Bothmeasurements were carried out at 20° C. The results are shown in Table5.

Comparative Example

A steel sheet was nickel plated, successively heat treated under thesame conditions as those of Example 1, and made into samples for thecomparative example, and the battery performance was evaluated in thesame manner as that of Example 1. The results are shown as Samples 19 to26 in Table 4.

Samples 19 to 21 correspond to Example 1. Samples 19 to 20 of thesesamples had a higher initial internal resistance than those of theExample 1 in the evaluation of the battery performance, as well asexhibiting 2 to 3A lower short-circuit current than those of Examples ofthe present invention. Sample 21 in which the inner surface was coatedwith graphite corresponds to Sample 9 and 10 of Example 1, and exhibiteda higher internal resistance and a lower short-circuit current thanthose of Examples of the present invention.

Samples 22 to 24 correspond to Example 2. Samples 22 to 23 of thesesamples had a higher internal resistance and a lower short-circuitcurrent than Samples 11 and 13. Sample 24 in which the inner surface wascoated with graphite had a higher internal resistance and a lowershort-circuit current than corresponding Samples 12 and 14.

Samples 25 to 26 correspond to Example 3. Sample 25 of these samples hada higher internal resistance and a lower short-circuit current thanthose of Sample 15, and Sample 26 had a higher internal resistance and alower short-circuit current then those of Sample 16.

POSSIBILITY OF USE IN INDUSTRY

As described above, the surface treated steel sheet of the presentinvention, in which a nickel-tin alloy layer is formed on the one sideof a steel substrate that is to become the inner surface of a batterycontainer, has effects such as a remarkably low internal contactresistance with the positive electrode mix and excellent alkalicorrosion resistance when it is used as the material for a batterycontainer.

In addition, the battery container of the present invention manufacturedby drawing etc., in which the above-mentioned surface treated steelsheet is adopted for use, has the excellent properties of a low internalresistance and high short-circuit current on the inner surface of thebattery container and a low contact resistance on the outer surface ofthe battery container.

Furthermore, the battery of the present invention, in which the batterycontainer of the present invention is used, has excellent batteryperformance such as a low internal resistance and high short-circuitcurrent.

                                      TABLE 1                                     __________________________________________________________________________                                condition of the                                                              heat treatment                                                           thickness                                                                          after plating                                                                         thickness of the constructional                                               layer                                                            of plating                                                                         heated                                                                            heated                                                                            Fe--Ni   Ni--Sn                                                                             Fe--Ni--Sn                  Sample                 Ni                                                                              Sn temp.                                                                             time                                                                              diffusion                                                                          Ni layer                                                                          alloy                                                                              alloy                       No.    Plating layer   μm                                                                           μm                                                                            ° C.                                                                       (min.)                                                                            layer (μm)                                                                      (μm)                                                                           layer (μm)                                                                      layer                       __________________________________________________________________________                                                      (μm)                     EXAMPLE 1                                                                     1      inner side                                                                         Ni--Sn alloy formation                                                                   1.8                                                                             0.09                                                                             500 360 1.86 0.43                                                                              0.16 --                                 outer side                                                                         Ni--Sn alloy formation                                                                   1.9                                                                             0.10       1.75 0.40                                                                              0.17 --                          2      inner side                                                                         Ni--Sn alloy formation                                                                   2.0                                                                             0.15                                                                             500 360 2.25 0.28                                                                              0.32 --                                 outer side                                                                         Ni--Sn alloy formation                                                                   2.0                                                                             0.74       1.96 0.15                                                                              0.60 --                          3      inner side                                                                         Ni--Sn alloy formation                                                                   0.5                                                                             0.36                                                                             500 360 0.53 --  0.61 --                                 outer side                                                                         Ni--Sn alloy formation                                                                   2.0                                                                             --         1.96 0.95                                                                              --   --                          4      inner side                                                                         Ni--Sn alloy formation                                                                   1.1                                                                             0.73                                                                             500 360 0.93 --  1.09 0.1                                outer side                                                                         Ni plating 1.8                                                                             --         1.9  0.8 --   --                          5      inner side                                                                         Ni--Sn alloy formation                                                                   1.9                                                                             0.74                                                                             300 360 --   1.7 0.73 --                                 outer side                                                                         Ni plating 2.0                                                                             --         --   1.8 --   --                          6      inner side                                                                         Ni--Sn alloy formation                                                                   1.9                                                                             0.76                                                                             600 360 4.41 0.28                                                                              0.81 0.40                               outer side                                                                         Ni--Sn alloy formation                                                                   4.8                                                                             0.75       5.40 0.15                                                                              0.60 --                          7      inner side                                                                         Ni--Sn alloy formation                                                                   1.9                                                                             1.52                                                                             500 360 1.25 --  0.70 --                                 outer side                                                                         Ni plating 2.0                                                                             --         2.02 0.9 --   --                          8      inner side                                                                         Ni--Sn alloy formation                                                                   3.9                                                                             2.53                                                                             500 360 2.35 --  2.98 --                                 outer side                                                                         Ni--Sn alloy formation                                                                   4.0                                                                             1.49       1.03 2.83                                                                              1.80 --                          9      inner side                                                                         Ni--Sn alloy formation                                                                   1.0                                                                             0.38                                                                             500 360 1.34 --  0.65 --                                 outer side                                                                         Ni plating 3.0                                                                             --         2.43 1.63                                                                              --   --                          10     inner side                                                                         Ni--Sn alloy formation                                                                   1.9                                                                             0.35                                                                             500 360 1.58 --  0.61 --                                 outer side                                                                         Ni plating 2.2                                                                             --         2.13 0.90                                                                              --   --                          __________________________________________________________________________

                                      TABLE 2                                     __________________________________________________________________________                            thickness                                                                     of plating condition of the                                                                      thickness of the                                           semi-      heat treatment                                                                        constructional layer                                       bright                                                                            bright after plating                                                                         Fe--Ni    Ni--Sn                                                                            Fe--Ni--Sn                                   Ni  Ni Sn  heated                                                                            heated                                                                            diffusion                                                                          Ni   alloy                                                                             alloy                Sample                  layer                                                                             layer                                                                            layer                                                                             temp.                                                                             time                                                                              layer                                                                              layer                                                                              layer                                                                             layer                No.     Plating layer   (μm)                                                                           (μm)                                                                          (μm)                                                                           ° C.                                                                       (min.)                                                                            (μm)                                                                            (μm)                                                                            (μm)                                                                           (μm)              __________________________________________________________________________    EXAMPLE 2                                                                     11      inner side                                                                         Ni--Sn alloy formation                                                                   0.9 1.2                                                                              0.09                                                                              500 360 1.85 0.42 0.15                                                                              --                           outer side                                                                         Ni plating 2.2 -- --          1.72 0.38     --                   12      inner side                                                                         Ni--Sn alloy formation                                                                   1.0 1.1                                                                              0.35                                                                              500 360 1.84 0.43 0.60                                                                              --                           outer side                                                                         Ni plating 2.2 -- --          1.73 0.39     --                   13      inner side                                                                         Ni--Sn alloy formation                                                                   0.5 1.5                                                                              0.70                                                                              500 360 1.78 0.40 1.08                                                                              --                           outer side                                                                         Ni plating 2.3 -- --          1.72 0.38     --                   14      inner side                                                                         Ni--Sn alloy formation                                                                   1.0 1.9                                                                              2.6 400 300 0.00 2.90 2.94                                                                              --                           outer side                                                                         Ni plating 2.3 -- 0.72                  1.28                                                                              --                   __________________________________________________________________________

                                      TABLE 3                                     __________________________________________________________________________                                   condition of the                                                                      thickness of the                                                      heat treatment                                                                        constructional layer                                        thickness                                                                          thickness                                                                          after plating                                                                         Fe--Ni   Ni--Sn                                             of Ni                                                                              of Ni--Sn                                                                          heated                                                                            heated                                                                            diffusion                                                                          Ni  alloy                         Sample               plating                                                                            plating                                                                            temp.                                                                             time                                                                              layer                                                                              layer                                                                             layer                         No.    Plating layer (μm)                                                                            (μm)                                                                            ° C.                                                                       (min.)                                                                            (μm)                                                                            (μm)                                                                           (μm)                       __________________________________________________________________________    EXAMPLE 3                                                                     15     inner side                                                                         Ni--Sn alloy plating                                                                   1.0  0.17 550 300 --   --  0.20                                 outer side                                                                         Ni plating                                                                             2.5  --           2.3  1.4 --                            16     inner side                                                                         Ni--Sn alloy plating                                                                   2.1  1.10 500 480 2.0  0.9 1.10                                 outer side                                                                         Ni plating                                                                             2.0  --           2.3  0.8 --                            17     inner side                                                                         Ni--Sn alloy plating                                                                   1.9  2.03 500 480  2.03                                                                               1.89                                                                             2.43                                 outer side                                                                         Ni plating                                                                             3.2  --           2.5  1.8 --                            18     inner side                                                                         Ni--Sn alloy plating                                                                   1.5  2.93 550 300 --   --  3.30                                 outer side                                                                         Ni plating                                                                             2.3  --           2.4  0.8 --                            __________________________________________________________________________

                                      TABLE 4                                     __________________________________________________________________________                                  condition of the                                                                           thickness of the                                          thickness                                                                            heat treatment                                                                             constructional layer                                      of     after plating                                                                              Fe--Ni    Ni--Sn                                                                            Fe--Ni--Sn                                  plating                                                                              heat                                                                              heated                                                                            heated                                                                             diffusion                                                                          Ni   alloy                                                                             alloy                Sample                 Ni Sn  treat-                                                                            temp.                                                                             time layer                                                                              layer                                                                              layer                                                                             layer                No.      Plating layer (μm)                                                                          (μm)                                                                           ment                                                                              ° C.                                                                       (min.)                                                                             (μm)                                                                            (μm)                                                                            (μm)                                                                           (μm)              __________________________________________________________________________    COMPARATIVE                                                                   EXAMPLE                                                                       19       inner side                                                                         Ni plating                                                                             1.1                                                                              --  none                                                                              --  --   --   1.1  --  --                            outer side                                                                         Ni plating                                                                             1.9                                                                              --               --   1.9  --  --                   20       inner side                                                                         Ni plating                                                                             1.9                                                                              --  none                                                                              --  --   --   1.9  --  --                            outer side                                                                         Ni plating                                                                             2.2                                                                              --               --   2.2  --  --                   21       inner side                                                                         Ni plating                                                                             1.0                                                                              --  none                                                                              --  --   --   1.0  --  --                            outer side                                                                         Ni plating                                                                             2.3                                                                              --               --   2.3  --  --                   22       inner side                                                                         Ni plating                                                                             1.0                                                                              --  done                                                                              500 360  1.7  0.3  --  --                                 and heat treatment                                                       outer side                                                                         Ni plating                                                                             1.9                                                                              --               2.1  0.9  --  --                                 and heat treatment                                              23       inner side                                                                         Ni plating                                                                             2.0                                                                              --  done                                                                              600 480  --   4.8  --  --                                 and heat treatment                                                       outer side                                                                         Ni plating                                                                             1.0                                                                              --               --   4.7  --  --                                 and heat treatment                                              24       inner side                                                                         Ni plating                                                                             1.2                                                                              --  done                                                                              500 360  1.6  1.0  --  --                                 and heat treatment                                                       outer side                                                                         Ni plating                                                                             1.9                                                                              --               2.3  0.2  --  --                                 and heat treatment                                              25       inner side                                                                         Ni--Sn alloy plating                                                                   2.1                                                                              0.05                                                                              done                                                                              500 360  1.9  --   0.09                                                                              --                            outer side                                                                         Ni plating                                                                             2.2                                                                              --               2.0   0.95                                                                              --  --                                             Ni--Sn                                                                        alloy                                                                         plating                                             26       inner side                                                                         Ni--Sn alloy plating                                                                   2.0                                                                              1.05                                                                              none                                                                              --  --   --   2.0  1.05                                                                              --                            outer side                                                                         Ni--Sn alloy plating                                                                   1.9                                                                              --  none                                                                              --  --   --   1.9  --  --                   __________________________________________________________________________

                                      TABLE 5                                     __________________________________________________________________________              graphite                                                                           battery performance                                                      coating                                                                            internal                                                                              short circuit current                                            on the                                                                             resistence (mΩ)                                                                 first                                                                              after 30                                                sample                                                                            inner                                                                              first                                                                             after 30                                                                          stage                                                                              days total                                              No. surface                                                                            stage                                                                             days                                                                              (ampere)                                                                           (ampere)                                                                           valuation                                    __________________________________________________________________________    EXAMPLE                                                                       1      1   none                                                                               101                                                                               125                                                                               8.3  6.7  good                                               2  none  98 115 8.0  7.2  good                                                3  none  99 113 8.4  7.5  good                                                4  none 100 117 8.2  7.6  good                                                5  none 101 119 8.2  7.4  good                                                6  none  97 120 8.1  7.3  good                                                7  none  95 118 8.4  7.5  good                                                8  none  96 105 8.6  7.6  good                                                9  existence                                                                           83 106 11.5 9.5  good                                               10  existence                                                                           79 105 11.8 9.8  good                                         2     11  none  85 110 10.7 9.0  good                                               12  existence                                                                           72 101 12.3 10.3 good                                               13  none  83 109 10.3 9.1  good                                               14  existence                                                                           70  99 12.5 10.1 good                                         3     15  none 102 120 8.2  7.2  good                                               16  none  98 115 8.7  7.1  good                                               17  existence                                                                           79  98 11.8 9.5  good                                               18  none  85 105 8.6  7.5  good                                         COMPARA-                                                                            19  none 125 143 5.6  4.0  poor                                         TIVE  20  none 122 139 5.7  4.4  poor                                         EXM   21  existence                                                                          109 119 9.3  7.8  poor                                               22  none 128 139 5.5  4.2  poor                                               23  none 125 142 5.6  4.3  poor                                               24  existence                                                                          103 112 9.4  7.7  poor                                               25  none 128 140 5.3  4.5  poor                                               26  none 101 137 8.6  4.1  poor                                         __________________________________________________________________________

What we claim is:
 1. A method of manufacturing a surface treated steelsheet for battery containers having an exposed outermost nickel-tinalloy layer, comprising the steps of:plating nickel on both surfaces ofa cold rolled steel sheet; plating tin on top of one surface of thenickel plated cold rolled steel sheet; and heat treating the nickel andtin plated cold rolled steel sheet to form a nickel-tin alloy layer asan exposed outermost layer.
 2. A method of manufacturing a surfacetreated steel sheet according to claim 1, wherein said step of platingtin comprises plating tin on top of both surfaces of the nickel platedcold rolled steel sheet.
 3. A method of manufacturing a surface treatedsteel sheet for battery containers, comprising the steps of:platingnickel on one surface of a cold rolled steel sheet to be later used asthe outer surface of a battery container; after said nickel platingstep, plating nickel-tin alloy on the other surface of the cold rolledsteel sheet to be later used as the inner surface of the batterycontainer; and heat treating the cold rolled steel sheet plated withnickel and nickel-tin alloy.
 4. A method of manufacturing a surfacetreated steel sheet according to claim 3, wherein said step of platingnickel comprises plating nickel on both surfaces of the cold rolledsteel sheet.
 5. A method of manufacturing a surface treated steel sheetaccording to claim 4, wherein said step of plating nickel-tin alloycomprises plating nickel-tin alloy on top of both surfaces of the nickelplated cold rolled steel sheet.
 6. A method of manufacturing a surfacetreated steel sheet for battery containers having an exposed outermostnickel-tin alloy layer, comprising the steps of:plating nickel-tin alloyon both sides of a cold rolled steel sheet; and heat treating the coldrolled steel sheet plated with the nickel-tin alloy as an exposedoutermost layer.